The need for cutting tool materials with improved toughness, good strength at elevated temperatures and chemical inertness capable of operating at high cutting speeds has generated a widespread interest in ceramic materials as candidates to fulfill these requirements. Conventional ceramic cutting tool materials have failed to find wide application primarily due to their low fracture toughness.
Therefore, many materials have been evaluated to improve ceramic cutting tool performance such as silicon nitride based composite cutting tools. Specific examples of silicon nitride based composite cutting tools are discussed in U.S. Pat. No. 4,388,085 to Sarin et al. (composite silicon nitride cutting tools containing TiC); U.S. Pat. No. 4,425,141 to Buljan et al. (a composite modified silicon aluminum oxynitride cutting tool containing refractory metal carbides, nitrides and carbonitrides); and U.S. Pat. No. 4,433,979 to Sarin et al. (composite silicon nitride cutting tools containing hard refractory carbides or nitrides of Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, and W). Many improvements have been made in the toughness, high temperature strength and chemical inertness, but increased demands by the cutting tool industry require cutting tools with new and improved characteristics. The present invention provides such a new and improved ceramic cutting tool.